A report Friday raises new doubts about Rep. Duncan Hunter’s claim that his opponent accepted contributions from an Islamic advocacy group, intensifying criticisms that the congressman has relied on a racist line of attack based on Democratic opponent Ammar Campa-Najjar’s Palestinian heritage in the final stretch of his campaign.

An attack ad casts Democrat Campa-Najjar’s contributions from the Council on American-Islamic Relations as part of a “well-orchestrated plan to infiltrate Congress.”

But a new review of Campa-Najjar’s FEC filings by the San Diego Union-Tribune uncovered no donations from CAIR. In order to maintain its status as a tax-exempt 501(c)3, the charity must limit its political activity. The paper did identify seven unpaid staffers or board members of CAIR or its chapters donating $17,300 to Campa-Najjar in 18 individual contributions.

CAIR is a large Muslim civil rights and advocacy group based in Washington, D.C. But Hunter and Breitbart, a far-right news site, have sought to link the advocacy group to terrorism. They point to a 2013 U.S. Department of Justice report naming CAIR as one of 300 “co-conspirators” with Hamas. CAIR was never indicted, and said its appearance in the report was due to overzealous prosecutors, the Union-Tribune reported.

The Campa-Najjar campaign noted to the Union-Tribune that the challenger has accepted far more in contributions, a total of $48,736, from J-Street, a Jewish political advocacy group. A spokesman for J-Street told the paper it “strongly rejects the notion that CAIR is supportive of Islamic extremism” and condemned Hunter’s attacks.

Campa-Najjar said he would not return the donations. “I reject the premise,” he told the Union-Tribune.

The race for the 50th District has become a national flashpoint as Democrats and other observers accuse Republicans across the country of campaigning on racial animus.

The Hunter ad ties Campa-Najjar, who is a Palestinian-Mexican American, to his paternal grandfather Muhammad Yusuf al-Najjar, a leading member of Fatah, the political party founded by Palestinian political leader Yasser Arafat. The candidate has renounced the actions of Yusuf al-Najjar, who died 16 years before the he was born.

“At best it’s desperate. That’s putting it mildly,” Campa-Najjar told the Guardian. He also called the attack “blatantly ignorant” and “unhinged from reality.”

The District is conservative — Inside Elections with Nathan L. Gonzales rates the race Likely Republican — but Hunter’s re-election was seriously jeopardized in August when he was indicted on charges of misusing campaign funds for personal expenses, including an Italian vacation and dental work.

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